In order to keep the compelling competition capabilities of the 3rd generation mobile communication system in the field of mobile communication system, its network performance must be improved and the network establishment and operation costs must be reduced. Therefore, the standardization working group of the 3rd Generation partnership Project (3GPP) is now working on the evolution of Packet Switched Core (PS Core) network and Universal Mobile Telecommunication System Terrestrial Radio Access Network (UTRAN) in order to enable the evolved PS Core network to provide higher transmission rate with shorter transmission delay, and to support mobility management among evolved UTRAN (E-UTRAN or EUTRAN), GSM EDGE radio access network (GERAN, wherein GSM is the abbreviation of Global System for Mobile communication, EDGE is the abbreviation of Enhanced Data Rate for GSM Evolution), UTRAN, Wireless Local Area Network (WLAN) and other non-3GPP access networks. This evolved mobile telecommunication system is called as Evolved Packet System (EPS), whose basic architecture is as shown in dashed block in FIG. 1. Each entity in FIG. 1 is described as follows:
User Equipment (UE) 101: a terminal capable of accessing two radio networks is called as a dual-mode terminal. The UE described in the present invention is a dual-mode terminal or multi-mode terminal that is capable of accessing a Universal Mobile Telecommunication System (UMTS)/GSM and an EPS networks.
E-UTRAN 102: an evolved radio access network, which can provide higher uplink and downlink rates with lower transmission delay and more reliable wireless transmission than GERAN/UTRAN. E-UTRAN includes network element eNodeB (Evolved NodeB) for providing radio resources for access of the terminal.
Serving Gateway (S-GW) 103: a user-plane entity, responsible for user plane data route processing.
Packet Data Network Gateway (PDN GW or P-GW) 104: responsible for the gateway function of UE accessing a Packet Data Network (PDN). P-GW and S-GW may be implemented in one physical entity.
Mobility Management Entity (MME) 105: a control-plane entity and a server for temporarily storing UE/user data, responsible for managing and storing UE context (for example, UE/user identifier, mobility management state, UE security parameters, etc.), and allocating a temporary identifier for the UE, and authenticating the UE when the UE currently camps in a tracking area or network managed by it.
Home Subscriber Server (HSS) 106: comprises Home Location Register (HLR) function, and stores basic data and service data of the subscriber.
Internet Protocol (IP) Multimedia Core Network Subsystem (IMS): an IP-based network architecture put forth by 3GPP, which establishes an open and flexible service environment, supports multimedia applications and provides rich multimedia services for users. IMS is an IP-based telecommunication network architecture and is irrelevant with access technology. In addition to providing services for the EPS, General Packet Radio Service (GPRS), WLAN and other packet access networks, it also provides services for the GSM, UMTS and other mobile cellular networks.
GERAN/UTRAN 107: the radio access network of legacy GSM/UMTS network.
Mobile Switching Center (MSC)/Visitor Location Register (VLR) 108: the two logically separated units, MSC and VLR, are typically implemented in one physical node in practical implementation and network deployment. The MSC/VLR may also be a new function entity MSC Server since R4 (Release 4) stage, which is uniformly denoted with MSC/VLR in the present invention.
Gateway Mobile Switching Center (GMSC) 109 is included.
Serving GPRS Support Node (SGSN) 110: a control network element of GPRS network, and its main roles are recording location information of the UE, and forwarding mobile packet data between a UE and a Gateway GPRS Supporting Node (GGSN).
When a UE camps on a GSM/UMTS network, the basic voice services and supplementary service based on voice services of the user are provided via Circuit Switched (CS) domain. The MSC/VLR and GMSC in FIG. 1 belong to CS domain network elements, and the user can perform voice call service and other services with users in the same network or other networks (such as fixed telephone network, and other mobile networks) via the CS domain. IP services are provided to the users via Packet Switched (PS) domain. The SGSN in FIG. 1 is a PS domain network element. The UE accesses the Packet Data Network (PDN) via PS domain. The operator's IP services network in FIG. 1 is a PDN.
In GPRS, the interface between MSC/VLR and SGSN is called as Gs interface. Gs interfaces is used for establishment Gs association between MSC/VLR and SGSN (i.e., the SGSN stores the VLR number and the VLR stores the SGSN number), and the MSC/VLR page the called UE via PS domain in the case the Gs association is established.
Gs association is established through combined Routing Area Update (RAU)/Location Area Update (LAU) (or attach/LAU). The combined RAU/LAU is that when a UE that supports simultaneous attachment to the CS domain and PS domain of GSM/UMTS network performs a RAU (or attach) in the PS domain, the UE includes an indication in the RAU (or attach) message; if the network supports Gs interfaces, the SGSN triggers a CS LAU procedure, and as such, a CS LAU procedure is included in a PS domain RAU procedure, and once the combined RAU/LAU ends, a Gs association is established between the SGSN and the VLR. When the UE moves around in the network, if there is SGSN change, in the VLR, the new SGSN number will be updated via a combined RAU/LAU procedure.
Once the UE is attached to the CS domain and PS domain of the GSM/UMTS network and a Gs association is established, the MSC/VLR implements paging for CS service(s) via the SGSN. In the present invention, paging for CS service is called as CS domain paging or CS paging. For example, when the user of the UE is called by a user of the local network or other networks, the MSC/VLR pages the UE through the CS paging flow as shown in FIG. 2. The flow is as follows:
201: a user of the UE has a call, and the user is a callee. The MSC/VLR receives the Initial Address Message (i.e., incoming call request) of this call;
202: the MSC/VLR initiates paging the UE. When paging the UE, the MSC/VLR determines that there is a Gs association, then the MSC/VLR sends a CS paging request message to the SGSN recorded in the Gs association;
203: after receiving the CS paging request message, the SGSN sends a corresponding PS paging message to GERAN/UTRAN, the message includes information such as the UE permanent unique identity (or called as International Mobile Subscriber Identity (IMSI)), and there is an identity in the message which indicates that the paging message comes from CS domain. This kind of paging message is also referred to as a CS paging message in the following text of the present invention. For example, when the signaling connection between a SGSN and a Radio access system is an IU connection, a RANAP paging (IMSI, TMSI (Temporary Mobile Subscriber Identity), paging area information, CS domain indication information) message is sent.
204: the GERAN/UTRAN receives the CS paging message, and sends a corresponding radio paging message (a CS paging request message) to the UE via air interface;
205: upon receiving the CS paging request message, the UE accesses CS domain of a GSM/UMTS network, and sends a CS paging response message to the GERAN/UTRAN;
206: upon receiving the CS paging response message, the GERAN/UTRAN sends a CS paging response message, for example, a RANAP Initial UE (paging response) message, to the MSC/VLR.
207: after receiving the CS paging response message, the procedure of establishing a CS call is started between the MSC/VLR and the UE. After the CS call is established, the user of the UE can start to have a conversation with the caller.
When UE camps on an EPS network via E-UTRAN, users' basic voice services and supplementary services which are based on voice service are mainly provided and controlled by IMS, and EPS system itself cannot provide or control voice call services, and can only provide transmission for IP data. However, during EPS network deployment process, some operators, without deploying or unwilling to deploy IMS, may deploy EPS networks to provide high-rate IP data services for the user in the key or hot spots where the GSM/UMTS network is also available. In this scenario, voice call services are desired to be provided and they can only be provided by the CS domain of the fully covered GSM/UMTS network, which means that the user cannot perform voice call service when the UE camps on the EPS network via E-UTRAN. In order to ensure that the user can make a voice call, a simple solution which also is the only one supported by 3GPP currently is that when the user performs a voice call, the UE is switched from accessing via an EPS network to via a GSM/UMTS network, and the voice service is implemented at CS domain of the GSM/UMTS network. This is called Circuit Switched fallback in Evolved Packet System (EPS) (CS fallback, CSFB).
The current method for realizing CS fallback is roughly as follows: Gs interface is introduced between MME and MSC/VLR. When the UE is powered on to access an EPS network via E-UTRAN, a Gs association is established between MME and MSC/VLR (storing the VLR number or address in the MME, and storing the MME number or address in the VLR). The newly introduced interface between MME and MSC/VLR may also be any extension based on Gs interface and principle, for example, SGs interface or Gs like interface, all of which are uniformly denoted with Gs interface. The association between MME and MSC/VLR may also be any extension based on Gs association principle, for example, SGs association or Gs like association, all of which are uniformly denoted with Gs association. Subsequently, when the UE moves around within the EPS network, the latest location information of the UE will be updated in MME, and if the serving MME of the area where the UE is currently located and the serving MME of the area where the UE is previously located are not the same, i.e., an MME change has occurred, then MME information stored in VLR will also be updated in time to the new MME number/address, ensuring that the MME information stored in the VLR is always correct.
When a voice call is performed, if the UE of the callee camps on EPS network via E-UTRAN, MSC/VLR sends a CS paging message to MME via Gs interface after receiving an incoming call request, then the MME performs CS paging after receiving the CS paging message, and the CS fallback take place upon receipt of a Paging Request message for the CS service. After CS fallback, the UE sends a CS paging response via the CS domain of the GSM/UMTS network and starts the process of call establishment with MSC/VLR, and after the call establishment is completed, the user of the UE can start to have a conversation with the caller. The CS paging flow when the UE is a called mobile terminal and it camps on the EPS network via E-UTRAN is as shown in FIG. 3.
301, the UE camps on EPS network via E-UTRAN, a Gs association has been established between MME and MSC/VLR, and the UE has registration information in both the MSC/VLR and the MME. The user of the UE has a call and the user is a callee. GMSC of the GSM/UMTS network where the UE is located performs a routing inquiry process upon receiving the Initial Address Message (IAM) (i.e., an incoming call request) of the call, and forwards the call to MSC/VLR. The MSC/VLR receives the incoming call request of the call;
302, upon receiving the incoming call request, MSC/VLR starts to page the UE of the called user. MSC/VLR sends a CS paging request message to MME according to information such as Gs association stored in VLR;
303-305, upon receiving the CS paging request message from the MSC/VLR, MME initiates a CS paging, and proceeds with the process of CS fallback;
306-308, after the CS fallback is executed, the UE accesses GSM/UMTS network and sends a CS paging response message to GERAN/UTRAN. GERAN/UTRAN sends the CS paging response message to MSC/VLR. The MSC/VLR starts a CS service call termination process.
The above FIG. 2 and FIG. 3 illustrate CS paging flows when the UE in GSM/UMTS network and EPS network respectively without introduction of Idle-mode Signaling Reduction (ISR) function or without activation of ISR, wherein the CS paging flow when the UE is in a GSM/UMTS network is as shown in FIG. 2 and the CS paging flow when the UE is in an EPS network is as shown in FIG. 3. In the circumstance of ISR activation, the UE cannot receive the call in some cases according to the above CS paging flows.
ISR-related concepts and problems of CS paging caused by introduction of ISR will be explained below with reference to FIG. 4 and FIG. 5.
ISR is a mechanism to limit signaling resulting from cell-reselection between Radio Access Technologies (RAT) performed by the UE when it is in idle mode. When the UE is in idle mode in an area overlapped with both GSM/UMTS network and Long Term Evolution (LTE) network, it may frequently switch between GSM/UMTS access mode and LTE access mode due to movement or changes of the intensity of radio signals or other reasons, which will cause frequent RAU (the procedure of the UE updating location in the PS domain of the GSM/UMTS network) and TAU (the procedure of the UE updating location in the EPS network) and will lead to a large amount of signaling interactions between the UE and the network. In order to reduce signaling load on the network brought about by the aforementioned signaling interaction process, one subject currently under study in 3GPP is ISR, the main idea of which is that when both the UE and the networks support ISR function, context information of the UE will be saved in both SGSN and MME, and registration information from these two networks is also saved in the UE, in this way, subsequently, when the UE switches among radio access networks, there will be no need for TAU or RAU.
FIG. 4 and FIG. 5 illustrate the problems of CS paging that need to be solved in the case that ISR is introduced. FIG. 4 illustrates a scenario of the problems, and FIG. 5 is the flow of attach and RAU procedure in the scenario as shown in FIG. 4, wherein ISR is activated in the procedure. The flow is as follows:
In the first step as shown in FIG. 4, a UE attaches in a tracking area 1 (i.e., TA#1 in FIG. 4) of EPS network. In this procedure, the UE sends an attach request to a MME, the MME interacts with the corresponding network elements and generates a tracking area list (e.g., TA#1 and TA#2 in FIG. 4) according to information such as the current Tracking Area Identity (TAI) of the UE, and sends the tracking area list to the UE in attach accept message. Upon receiving the attach accept message, the UE stores the tracking area list and sets the indication which indicates UE has been updated in the EPS network. After the attach procedure is completed, the UE is registered in the EPS network, HSS stores MME identity and VLR number, and what is currently recorded in the Gs association in VLR is MME;
The first step shown in FIG. 4 includes the following parts of attach flow in FIG. 5:
501, the UE performs attach procedure in TA#1 of the EPS network, and sends an attach request message to MME via an eNodeB, wherein the message includes information such as user identity and TA#1;
502, the MME receives the attach request message sent by the UE, and performs operations such as authentication on the UE, then sends an update location request message to HSS, wherein the message includes MME identity and IMSI;
503, after receiving the update location request message sent by the MME, the HSS performs the procedure of insert subscriber data, in which the HSS stores MME identity and IMSI and inserts the subscription data into the MME;
504, after insertion of subscription data is completed, the HSS transmits an update location response message to the MME;
505, according to information that it itself supports Gs interface and the subscription data etc. information, MME determines that it is necessary to send an update message to MSC/VLR, so MME sends a location update request message to MSC/VLR, wherein the message carries information including MME identity and IMSI;
506, MSC/VLR receives the location update request message sent by the MME, and stores the MME identity carried in the message, and a Gs association with the MME is established in the MSC/VLR; MSC/VLR sends the update location request message to HSS, the message includes VLR number and IMSI;
507, HSS receives the update location request message sent by MSC/VLR, and performs the procedure of insert subscriber data, in which HSS stores VLR number and IMSI and inserts the subscription data into the MSC/VLR;
508, when insertion of subscription data is completed, the HSS sends an update location acknowledgement message to the MSC/VLR;
509, after the MSC/VLR completes the procedure of location update, the MSC/VLR sends a location update acknowledgement message to the MME. The MME stores the VLR number information in step 505 or at this moment, and a Gs association with the MSC/VLR is established in the MME;
510, the MME generates a tracking area list based on the current tracking area information etc., wherein the tracking area list generated by the MME in the case as shown in FIG. 4 includes TA#1 and TA#2, the MME sends an attach accept message to the UE, wherein the message includes the above tracking area list and UE identity information allocated for the UE in the MSC/VLR and MME;
The second step shown in FIG. 4 is that when the UE moves from EPS network to a area covered by GSM/UMTS network, UE performs cell reselection due to reasons such as signal quality, accessing from GSM/UMTS network routing area 1 (i.e., RA#1 in FIG. 4) and performs a combined RAU/LAU procedure. In this procedure, since SGSN, MME and UE all support ISR function, ISR is activated, MME continues to store the data such as UE context, SGSN sends a combined RAU accept message which includes an ISR activation indication to the UE, and UE receives the message, identifying that UE registers in both EPS network and PS domain of GSM/UMTS network. After combined RAU/LAU is completed, ISR is activated, UE has registered in both PS domain of GSM/UMTS network and EPS network, wherein it registers in tracking areas TA#1 and TA#2 in the EPS network and registers in RA#1 in the PS domain of GSM/UMTS network, HSS stores information including MME identity, SGSN number and address and VLR number, and what is currently stored in Gs association in VLR is SGSN number;
The second step shown in FIG. 4 includes the following parts of the combined RAU/LAU flow in FIG. 5:
511, the UE moves from TA#1 of E-UTRAN to RA#1 of GERAN/UTRAN to access the networks, and since RA#1 does not register in the network, the UE sends a RAU request message to SGSN, wherein the message includes network capability of UE, UE location information, UE identity information and combined RAU/LAU indication. Network capability of UE includes an ISR indication, which indicates that the UE supports ISR function;
512, SGSN deduces MME address information according to information such as UE location included in the RAU request message, and sends a context request message to the MME, wherein the message includes UE and the current SGSN address. According to the requirements of the latest prior art, SGSN needs to store MME address information, so here the SGSN may store the MME address information;
513, after receiving the context request message, the MME transmits a context response message to the SGSN, sending the stored context information to the SGSN. If the MME is able to activate ISR for this UE, then the message includes ISR identity information. According to the requirements of the latest prior art, MME needs to store SGSN address information, so here, the MME may store the SGSN address information included in the received context request message;
514, the SGSN sends a context acknowledgement message to the MME, wherein the message includes ISR identity, indicating that the SGSN also supports ISR function and ISR activation condition is satisfied, so ISR function is activated, indicating the MME to continue store information such as context of the UE. If the message does not include ISR identity, the MME will mark that the information in HSS and S-GW are invalid;
515, the SGSN sends an update location request message to HSS, wherein the message carries information including SGSN number, SGSN address and IMSI;
516, after receiving the update location request message sent by the SGSN, the HSS performs procedure of insert subscriber data, in which the HSS stores SGSN number, SGSN address and IMSI, and inserts the subscription data into the SGSN;
517, when insertion of subscription data is completed, the HSS sends an update location acknowledgement message to the SGSN;
518, the SGSN sends a location update request message to MSC/VLR according to the facts that Gs interface is supported and the current update is combined routing area/location area update, wherein the message includes information such as SGSN number and IMSI. After receiving the location update request message sent by SGSN, the MSC/VLR stores the SGSN number, and at this moment, a Gs association with the SGSN is established in the MSC/VLR;
519-521, if the current location area of the UE in the GSM/UMTS network and the location area when it is in the EPS network belong to different MSC/VLRs, MSC/VLR interacts with HSS to perform operations such as insert subscriber data, HSS inserts the subscription data into the new MSC/VLR, and new VLR number and UE location information are stored in the HSS, while the UE information in the old MSC/VLR will be deleted. If MSC/VLR does not change, then the processes in steps 519-521 will not be performed;
522, after completing the procedure of location update, the MSC/VLR sends a location update acknowledgement message to the SGSN. The SGSN stores VLR number in step 518 or at this moment, and a Gs association with the MSC/VLR is established in the SGSN;
523, the SGSN sends a RAU accept message to the UE, wherein the message includes ISR identity information, which tells the UE that currently ISR is already activated, the registration information of the UE in EPS network (e.g., the tracking area list and identity of the UE allocated in EPS network) is remained valid in the network, and the registration information of the UE in the EPS network should also be remained valid in the UE. At this moment, UE registers in both EPS network and PS domain of GSM/UMTS network. If the RAU accept message does not include ISR identity information, this indicates that ISR is not activated, and UE will set the registration information in EPS network to be invalid upon receiving the RAU accept message, then the UE registers only in the PS domain of GSM/UMTS network;
Now, the UE is in a state that in both MME and SGSN the UE are registered and ISR is activated (i.e. ISR is active). If the UE subsequently moves to a legacy SGSN (e.g., a SGSN before Version 8) network that does not support ISR function, ISR function will become inactivated, the UE information etc. in the EPS network will be deleted by MME, and it will also be set in the UE that EPS network is not registered, i.e., the UE only registers in PS domain of GSM/UMTS network. If, afterwards, the UE moves from this network area controlled by SGSN that does not support ISR function to a network area controlled by SGSN and MME that supports ISR function, ISR function will change from being inactivated to being activated after performing RAU and TAU.
As described above, ISR being activated means that in the case that UE and the networks both support ISR function, the UE stores information on the registration of UE in both EPS and GSM/UMTS networks, and MME and SGSN both store UE information and ISR activation indication, and the MME has an ISR relation with the SGSN for the UE (also named as ISR-associated). ISR being inactivated means that only information on registration of UE in EPS or PS domain of GSM/UMTS is kept valid in the UE, and only MME or SGSN keeps the UE information valid. When the UE moves at an edge covered by several networks or in an area where several networks overlap, ISR function may constantly change between being activated and being inactivated.
The third step in FIG. 4 is that: when the UE moves from RA#1 of GSM/UMTS network to TA#2 of EPS network, since UE has registered in the EPS network, and the current tracking area TA#2 is in the registered tracking area list stored by the UE, the UE will not initiate TAU any more when ISR is activated according to the prior art, and thus the Gs association stored in the MSC/VLR will not be updated. In other words, when the UE accesses in TA#2, the UE camps on an EPS network via E-UTRAN, the Gs association in VLR should record MME information, but actually what is recorded in the Gs association in VLR is SGSN number.
When the UE subsequently moves between TA#1, TA#2, and RA#1, the UE will not initiate TAU or RAU any more, so the networks will not know whether the UE is currently in an EPS network or in a GSM/UMTS network. Assuming that when the UE is in TA#2, the user of the UE has a call and the user is the called user, and MSC/VLR needs to page UE via Gs interface, MSC/VLR will send a CS paging to SGSN according to the Gs association recorded in VLR, and the SGSN will trigger a paging in PS domain of GSM/UMTS network, but since the UE currently only camps on the EPS network via E-UTRAN, UE cannot receive the paging in the PS domain of GSM/UMTS network, i.e., the user of the UE is unable to receive the CS call in this case.
In the scenario as shown in FIG. 4, if UE is in RA#1, MSC/VLR needs to control CS paging performed in GERAN/UTRAN via SGSN; if UE is in TA#1 or TA#2, MSC/VLR needs to control CS paging performed in E-UTRAN via MME. However, when the CS paging is performed in the case of ISR activated, the network cannot determine whether the UE currently camps on E-UTRAN or GERAN/UTRAN, therefore, it needs to page UE via E-UTRAN and GERAN/UTRAN in order that the UE receives the CS paging.
A method for solving CS paging in ISR activated case in the prior art is that two Gs associations with SGSN and MME respectively are stored in MSC/VLR, and when CS paging needs to be performed, as shown in FIG. 6, MSC/VLR sends a CS paging message to SGSN and MME respectively according to the two Gs associations stored in VLR, and SGSN and MME respectively initiate a CS paging procedure in GERAN/UTRAN and E-UTRAN.
However the solution has the following requirements and problems: MSC/VLR needs to store two Gs associations with SGSN and MME respectively; both SGSN and MME need to send ISR identity information etc. to MSC/VLR when performing RAU and TAU, which changes the existing interface; MSC/VLR needs to process differently according to two situations of ISR being activated and being inactivated in a location update message; MSC/VLR needs to deal with various cases of changes between ISR being activated and being inactivated that may be caused due to UE accessing in different network areas controlled by different SGSN and MME; MSC/VLR needs to initiate two CS paging procedures when performing CS paging; if an embodiment in which MSC/VLR does not need to know whether ISR is activated or not is adopted, and if UE has camped in both EPS via E-UTRAN and GSM/UMTS networks, MSC/VLR will store and maintain two associations even if in the case that ISR is not activated, until MME or SGSN sends an informing message to the MSC/VLR due to the reason that MME or SGSN does not interact with the UE for a long time or the UE is detached from the network, or the MSC/VLR does not delete invalid association information and end the corresponding processing unless the MSC/VLR fails in CS paging via MME or SGSN. The CS paging solution in which MSC/VLR maintains two Gs associations and initiates two paging procedures does not only need to upgrade MSC software when implemented, but may also increase requirement of capacity and signaling processing capability of MSC/VLR. Moreover, if the UE can not be served by the same MSC/VLR when the UE camps in EPS network via E-UTRAN, or in GSM/UMTS network, it will not be possible to store both Gs associations with MME and SGSN in the corresponding MSC/VLRs to MME or SGSN. The above requirements all increase the complexity of MSC/VLR, and in a scenario that the network needs to support both ISR and CS fallback, the operator has to upgrade the MSC/VLR in existing network, which may have risks and affect user experience during upgrade. If MSC/VLR need to be upgraded to increase its capacity and signaling processing capability, costs will be increased for device providers and operators, thus affecting commercial application of techniques such as CS fallback and ISR, as well as EPS network.